Landing gear construction



\ w. H. HOGAN LANDING GEAR CONSTRUCTION Filed Nov. 14, 1955 Aprilv 21, 1959 2,883,181 Patented Apr. 2l, 1959l United States Patent Oiilice LANDING GEAR CONSTRUCTION n Application November 14, 17955, serial No'. 546,722

z claims. (cl. 267-64) This invention relates'to `liquid springs in general and more particularly' to anew and improved liquidspring device particularly suited i for" use in aircraft landing gears. t i n An aircraft landing gear must serve two functions, one of which is to absorb the impact of landing and the other is to` provide resilient support for thery aircraft when it is moved on theground. An aircraft landing gear according to this invention isparticularly desirable since it provides means for'serving `both lof the above named functions while `providing a mechanismlwhich is Vlighter and smaller than comparable conventional landing gears.

Itis an important object `of this" invention to provide a landing gear incorporatinga liquid spring equipped with motion damping means particularly suited for absorbing landing pactsand resiliently supporting `the aircraft when it is on the ground.

It is another object of this invention to provide along stroke liquid spring in combination with integral motion damping means. w i w Itis still another object of this invention tof provide an aircraft landing gear incorporating a new and improved liquid spring and shock absoribing device.

Further objects and advantages will appear from the following description and drawings, wherein "i Figure 1 is a side elevation inI longitudinal` sectio showing a landing gear according to this invention in the fully extended position; ,w

`Figure 2 is an enlarged vfragmentary llongitudinal 'sec-L tion vof the motion damping means; and f 'u Figure 3 is a view similar to Figure 2` showing the po?` sition` of the elements when the landing gear sfully corn-1` pressed. Y L

`Referring to the drawings, the preferred landing gear `is providediwith an `upper telescoping member j formed with -trunnions 11 utilized toA mount the landing gear on the aircraft. Ailower telescoping member`12 isaxial ly movable relative to the uppertelescoping member 10, and is provided `with a.: ground4 engaging wheel13 journaled on its' lower end. A bearing 14 threaded onto the upper end of the lowei telescoping meinberlZ cooperates with a r bearing 16 mounted ontherjupper telescoping member 10 Abya gland nut 17, toV provide lateral support between the two telescoping members while permitting relative `axial motion therebetween. To `prevent relative rotation between the two telescopingmembers,torque anns 18 are pivotally connected between thefftwofteleber'12, l mount on scoping members as at 19 and 21,.- LA spacersleeve 22 t is positioned `within the upper telescopingmember 101between "the bearings 14 and 16 to limit axial motion of the bearing 14 toward the bearingI 16'v and thereby limit theextension ofthe strut,... :j 7 f The lower telescoping member 12 is formed with an axially extending bore 23 terminating in an end wall 24 at its lower end. A plunger tube 26 projects into the upper end of the bore 23 through a gland member 27 which in turn is mounted at the upper end of the lower telescoping member 12. The plunger tube itself is formed with an axial bore 28 extending from its lower end and on its lower end with an outwardly extending tlange 29 slidably mounted within the bore 23 of the lower telescoping member 12. The closed upper end `30 of the plunger tube 26 engages a radial wall 35 formed in the upper telescoping member 10 to limit axial motion of the plunger tube in the upward direction. A metering pin 31 is threadedlyconnected tothe end wall 24 at its lower end and is provided with a head portion 32 which projects into the bore 28 of the plunger tube 26. t Re# silient seals 33 and 33a are providedi on the head portion 32 and on the gland member 27 respectively to prevent leakage of fluid from the bore 23 along the plunger tube y26. Thus a cavity is formed with a lower telescoping member 12 which Lis filled with liquid and divided intoaiirst or lower chamber 34 and a Vseconderupper chamber 36. It should -be understood that `the cavity which includes both of the chambers 34 and 36 is com'- pletely lilled with liquid when the landing gear is in the extended position of Figure l and is under a precharge pressure at this time. The zone within the: plunger tube 26 above the seal 33 and the zone above the lower telescoping member 12 within thel upper telescoping member w10 are vented through apertures 40. Preferably the seal 33 on the head portion" 32 is radially within the seal 33a on the gland member 27 so that there will be no pressure forces produced onf the inside of the plunger tube 26 which are not balanced by iluid pressures on the outside of the plunger tube or vice versa.

To provide for damping toiresist movement `of the plungertube 26 relative to the `lower telescoping mem-1 the plunger` tube` adjacent to its lower end an orice plate 37 by means of asnap `r' in'g38. The orifice plate is formed with a` central `oriiice 39 affording a` circular passageway around the metering pin 31 through which Huid can flow from the lower chamber 34v to the upper chamber 36 when the plunger tubeV moves axially into Athe lower telescoping member `12`.` "Asealf41 is provided on the flange 29 so that the oilyrlluid com-` munication between the two chambers is: through the orifice 39. The plunger tubevis formed with a plurality of radial openings 42 adjacent `to the orifice plate 37'to provide iluid communication between "the "chamber 36 and the portion of the bore 28 below thehead 32, which portion is to be understood as apart of the chamber' 36. ,Inthe operation of this device there are two types: of reaction forces that operate on the plunger tube 26 when it moves into the lower telescoping member 12, one of whicllis determined by the motionof the plunger tube 26 and the other by-the amount theplungerftube` 26 prof4 jects yinto the liquid lled cavity. `When ltherplunger tube4 26 moves toward the lower telescoping,memberlkthe volume of the lower chamber 34 is decreased and the vola umejof the upper chamber 36 isincreased; Therefore,n the liquid pressure in fthe lower,` `chamber increases rapidly the liquid pressure in the` upper chamber 36 de.-` creases` This difference in pressure producesalreaption; forceonthe flange 29 of the `plunger-tube whichf resists: movement thereof. Thediierence pressure between the'two chambers34 and,36 `also causes the liquidin the lowercharnber 34de flow through the orifice-39 into y'the upper chamber 36. Therefore, the ilow; of liquidlthrough th'e` orice attemptsto equalize the1pressure of-.thefliquid in` the twochambers.- The difference in pressure betweeni the-twoehambers e4, and 36 is therefofedetermied by? way. as the plunger tube 26 moves relative to the lower telescoping member.

Preferably the metering pin 31 is formed with a first portion "43 (Figurei 12) having Aay cross section 'onlyi slightlyrsmaller th'an the area of the orice- 39-whichis positionedv Within theorifice when they landing gear'is inthe fully extended* position. Therefore, avery high restrictiona'isfprovided to'fresist the flow of liquid from the first chamber 34-to the second chamber`36 during the initial landing of the-aircraft, that is when'the plunger tube initiallyy moves into 'the lower telescoping member 12. Immediately below the first portion 43, the metering pin is contoured to cooperateiwith 'the orifice 39-to provide a-HvaryingI flow restriction so that the desired load stroke will'be achieved in thelanding gear.

Once the plungertube-ZG stops moving, relative to the lowertelescoping member 12, the liquid pressure 'in the twolchambersequalizes andther liquid spring force is the only-liquidA forceeffective onthe plunger tube 26. It should be understood that movement of flange 29 per se does notproduce a difference in the total volume of the two chambers 34 fand 136, that is, the volume of the liquid cavity. The total volume `of the cavity is therefore only affected by the'relative position of the plunger tube 26 an'dfvthe lower telescoping member 12. If'the plunger tube 26 is moved into `the lower telescoping member 12, the' total volume of the cavity is reduced by an amount equalto the effective cross section of the portion of the plunger' tube 12 passingthrough the seals 3.3 and 33a times the length of the' portion of the plunger tube moving into the lower telescoping member. Thus the total volume of the cavity is determined by the relative position of the plunger tube and the lowertelescoping member 12 and is not affected-by the relative velocity therebetween. As the plunger tube 26 is moved axially into the lower telescoping member 12, thetotal volume of theV liquid cavityisdecreased so that liquid is compressed toa higher pressure. This increases the reaction force of the liquid on the plunger tube-so a resilient liquid spring is provided.

Since a very small amount of compression in liquid causes a very largen increase in pressure, it is necessary to provide a devicewherein theplunger tube has a relatively "small cross-sectional area if it is desired to achieve a relatively longspring stroke. However, since the plunger tube26-is subjected to axial loading, the strongest column will be provided, for a given cross sectional area, if a hollowv tube Iconfiguration is used.

In a normal landing, the upper telescoping member 10 moves axially towardthe lower telescoping, member 12 and thereby moves the plunger tube 26 into the lower telescoping member 12. The majority of the impact enei'gy is absorbed by. the flow of liquid from the lower chamber 34fto the upper chamber 36. However, after the landing impact, the aircraft-is resiliently supported by the 'liquid spring action.

`By`utilizinga metering pin 31 formed with the enlarged rst portion 43', it is possible to cause a rapid loading of the landing gear at impact which causes the tires of the wheel 13"to"absorb the initial energy after which the remaining portionof'the impact is absorbed by the flow of liquidthroughthe orifice '39l andthe compression ofthe liquidwithin the lower telescoping member 12.

Since'falliquid spring maybe small for a` givenl load when comparedto-pneumatic springs or the like because ofthe higher operating pressures, a landing gear accord# ing=to=this"inventionmay belighter and more compact thanfwas previously possible in pneumatic spring 'type landingwgearsrx Also, since thev plunger tube 26 -is a hollow column, a'relatively'long stroke can be achieved without sacrificing the column strength of the plunger tube. Of course the use of a hollow plunger tube makes it possible to incorporate a contoured metering pin so that any given load stroke relationship may be achieved.

Although a preferred embodiment of this invention is illustrated, it will be realized that various modifications of the structural detailsm'ay be made without departing from the modeofoperationf and the essence of the invention. Therefore, except insofar as they are claimed in the appendedclaims, structural details may be varied widely without modifying' the mode of operation; Accordingly, the appended claims and not the aforesaid de tailed description are determinative of the scopel of the invention.

I claim:

l. A liquid spring comprising a member formed with an axial bore, a plunger tube projecting into said bore, first sealfmea'nsfi'xed relative to said member sealing against'theouter surface of said plunger tube, a solid metering pin'vmounted4 on said -member projecting into said plunger tube, second seal means mounted on said metering.j pin'sealing against the4 inner surface of said plunger tube, a liquid filled cavity in said member defined in part by said1plunger tube the volume of which is changed-only by relativemotion between said plunger tube and member, an orifice plate mounted on said plunger tube formed with acentral -orifice through `which said metering pin projects, lsaid orifice plate dividing said cavity into two chambers in fluid communication through said orifice, said lmetering pin being contoured to regulate the resistancefto flow 'of liquid through said orifice.

2. A landing gearA adaptedvto absorb landing impacts comprising upper :and lower telescoping members capable of relative axial motion, bearing` means between said members preventing lateral motiontherebetween, said upper member being adapted-to be mounted on an aircraft, a ground engaging element mounted on said lower element, one of saidmembers being formed with an axial bore, aplunger tube with-one end projectinginto said bore, a seal fixed relative` to said one member sealing against the outer surfaceofsaid plunger tube, a metering pin fixed on saidone member extending into said plunger tube, a seal `fixed on said metering pinsealing against the innersurface of said plunger tube, said seals, one member and plunger tube co-operating todefine a liquid filled cavitypan orifice plateon said plunger tube formed with an orifice through which said metering pin` projectsy dividing said cavity intoftwo chambers in fluid communication through said orifice, said metering pin being contoured to regulate the resistance to flow through said orifice, the other of said members being formed with a radial surface facing said bore, the'othery end of said plunger tube engaging .said radial surface `limiting axial motion of said plunger tube -relativerto-said other member only ina direction away from said one member.

Rfrences cited ifi the me of this patent UNITED STATES PATENTS 

